1. FIELD OF THE INVENTION
This invention relates to haze-free polymeric dispersant additives for lubricating oils which may also be useful as viscosity-index improvers for lubricating oils. More particularly, this invention relates to haze-free solutions of substantially saturated polymers comprising ethylene and one or more C.sub.3 to C.sub.28 alpha-olefins, preferably propylene, which have been grafted in the presence of a free-radical initiator with an ethylenically-unsaturated carboxylic acid material preferably at an elevated temperature and in an inert atmosphere, and thereafter reacted first with a polyfunctional material reactive with carboxy groups, such as (a) a polyamine, (b) a polyol or (c) a hydroxy amine, or mixtures thereof, to form multifunctional polymeric reaction products and thereafter with at least a haze preventing amount of an oil-soluble acid.
2. DESCRIPTION OF THE PRIOR ART
It is well known that the introduction of carboxylic acid groups onto ethylene copolymers provides a means for derivatizing said copolymers. One means of introducing the carboxylic groups is by grafting of maleic anhydride onto said polymer as by a free radical mechanism.
Belgian Pat. No. 843,360 teaches the production of soluble, sludge-dispersing additives for hydrocarbon fuels and lubricating oils by the free-radical induced grafting in solution of an ethylenically-unsaturated dicarboxylic acid material such as maleic anhydride onto a substantially saturated copolymer comprising ethylene and at least one other alpha-olefin at an elevated temperature to provide, without substantial polymer degradation, a useful precursor copolymer which can be subsequently reacted with a carboxylic acid reacting polyfunctional material, such as a polyamine, a polyol or a hydroxyamine or mixtures of these, to form multifunctional polymeric derivatives having particular utility as engine sludge and varnish control additives for lubricating oils.
It is often found that during the preparation, processing and storage of these various oil-soluble grafted hydrocarbon polymers a haze develops in their oil concentrates. The source of this haze does not appear to be the same as that haze resulting from incompatibility of the several additives in a lubricating oil additive concentrate (see U.S. Pat. No. 3,897,353 wherein haze resulting from component incompatibility is overcome in a lubricating oil additive concentrate by blending an amorphous ethylene-propylene copolymer with an N-alkyl methacrylate containing polymer) but rather, the haze appears the result of oil-insoluble, infilterable and therefore undesirable by-products of the graft reaction. German DOS No. 2,634,033 teaches that the grafting of olefinic copolymers with an ethylenically unsaturated, polar nitrogen containing monomer, e.g. 2-vinyl pyridine, yields a homopolymer as a highly undesirable by-product of most graft reactions.
It is an object of this invention to provide a haze-free, grafted ethylene copolymeric dispersant, generally useful as a mineral oil viscosity index improver of increased sludge performance and/or enhanced thickening activity.